from my brain
RS: B18B1 motor, base model. no moonroof, no power locks, no ABS, no cruise control, no life. power windows.
LS: B18B1 motor, upgraded. moonroof, power locks, ABS, cruise. power windows. same interior (year depending). alloys (98+ standard)
GS: B18B1 motor. upgraded. same as LS with leather seats, cd-player, alloy wheels.
LS is the most common non-VTEC integra.